There are several instances in which it may be desirable to track and or estimate the location of individual units within a network. In at least some of these instances, some of the more traditional methods, such as global positioning systems (GPS), may have difficulties. One such example includes, when the units being tracked are located internal to a building. This is because GPS signals may have difficulties penetrating the walls of a building and/or traversing other obstructions. In some of the same or other instances, there may be an insufficient number of range measurements relative to one or more reference units, whose locations are either known or determined, to allow for the position of a particular unit to be triangulated.
In at least some of these instances, it may be possible to use measured range information between at least some of the units to allow a location estimate to be determined for one or more units. In at least one such instance, an error value associated with the estimate including, in at least one instance, a sum of the square of the differences between the measured range information, and the range information corresponding to the computed spatial between a pair of units, and associated with a set of estimated locations is minimized, through an iterative minimization process. At least one such example of a corresponding system and method is described in Patwari et al., U.S. Pat. No. 6,473,038, the disclosure of which is incorporated herein by reference. However, in some instances, depending on how the initial location estimate is selected, an iterative approach, which minimizes an error value may become trapped in a local minimum, and have difficulties converging to a more accurate solution. Consequently, it would be beneficial to develop an approach, which is more likely to identify a solution, which avoids a local minimum solution.
The present inventors have recognized that an approach, which selects a plurality of different sets of initial location estimates, which are each used to iteratively estimate a location for each of a plurality of units in a network, would be beneficial in arriving at a solution, which more readily avoids any local minimums. Of the plurality of location estimates, which are determined, the solution set having the smallest error value is selected and used as the location estimate for the plurality of units. The present inventors have further recognized that it would be beneficial for the different sets of initial location estimates to be selected from a possible location area determined for each of the units. In this way, a system and method for improved location estimation accuracy can be provided.